1. Field of the Invention
The present invention relates to a substrate for semiconductor package and a wire bonding method using thereof.
2. Description of the Related Art
In general, “wire bonding” refers to a process wherein a semiconductor die, which is separately sawn from a wafer, is attached on a substrate using adhesive, and a bond pad, which is formed on the semiconductor die, is electrically connected to electrically conductive patterns, which are formed on the substrate.
The wire bonding is performed using a wire bonder, which comprises a camera for recognizing the coordinates of the substrate and the semiconductor die; a PRS (pattern recognition system) for processing images recognized by the camera and calculating a changed wire bonding coordinate; and, a capillary for performing bonding in accordance with the changed wire bonding coordinate. The PRS compares pre-stored reference coordinates with actual coordinates, which are photographed by the camera, so that wires can be bonded at the changed coordinate. Specifically, the PRS makes it possible to determine, before wire bonding, whether the coordinates of the substrate and the semiconductor die correspond to the pre-stored coordinates, as well as how much the coordinates should be modified, if they do not correspond.
Meanwhile, the substrate is provided with a number of electrically conductive patterns having bond fingers, a power ring, a ground ring, and the like. The bond fingers, the power ring, and the ground ring are not coated with a solder mask and are entirely opened for easy wire bonding. In addition, the substrate is additionally provided with an entirely-exposed fiducial mark so that the PRS of the wire bonder can determine whether the substrate is positioned in any location, where it is connected with the electrically conductive patterns, the power ring, or the ground ring or not. Furthermore, certain regions of an outer peripheral edge of the substrate are not coated with the solder mask, including, as mentioned, the bond fingers, the power ring, the ground ring, and the fiducial mark, in consideration of the tolerance of the solder mask. This type of solder mask is referred to as an NSMD (non-solder mask defined).
Therefore, the wire bonder checks the fiducial mark first, determines if the substrate is correctly positioned and how much the coordinates should be modified, if any, and performs wire bonding.
However, such an NSMD type of substrate has a problem in that, considering the tolerance of the placement of the solder mask, the bond fingers, the power ring, the ground ring, and the fiducial mark should always be spaced more than a predetermined distance from each other. This makes it difficult to make the substrate in a compact size.